The man behind Upton's enviable physique, celeb-loved trainer Ben Bruno, caught up with E! News exclusively to dish about the ins and outs of her fitness and diet routine ahead of the nearly-nude shoot. Bruno told us Kate was "very disciplined" on the training front, and committed to working out twice a day for between five and six days a week.

Bruno shared the two would focus on weight-training in the morning and cardio in the afternoon, though he stressed the importance of switching up workouts to avoid the monotonous routine of hitting the gym hour after hour.

"A lot of times in the afternoons, we would either go together or she would go with her dog, Harley, hiking just to get outside," he revealed. "Or, for a while when we were really amping up for the shoot, we would do an hour of tennis every day."

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Ben also emphasized the importance of lifting weights and circuit training throughout their 60-minute sessions as a primary tool in shaping Upton's curves, adding that the SI covergirl can deadlift an impressive 200 pounds and has pushed 540 pounds on the sled.

"I've personally see Kate already inspire a lot of girls to [lift] heavier because in their mind they think that they're going to get big and bulky, but then they see Kate doing it and think, 'Well, I guess I don't have to worry about that,'" he explained.

When it comes to balancing strength training and cardio, Bruno offered this helpful analogy: "Strength training is your main course and the cardio is your side dish. So, both have their place at the table, but strength training is really the crux of what she did and what I think women should do to change their body."

And speaking of dishes, Bruno admitted Upton's nutrition plan stressed high protein and veggies, limited sugar and carbs, but most importantly, balance!

"It wasn't so much about going on a diet just for the shoot," Bruno stressed, adding, "It was about making healthy lifestyle changes that are easy to maintain because it's not drastic."

"She made time here and there for treats," he dished. "It was mostly healthy, but also some fun. Kate likes her wine and sweets. It's just about moderation."

"We made a pact, a pinky promise that she would do it the healthy way," Bruno admitted. "I'm proud of her hard work, but I think that a lot of times people get really obsessive when they have [big events coming up], but she kept a really good job of living a balanced life."